This invention relates to a sprue gated injection molding nozzle and a method of making it having an integral electrical heating element, a forward end portion of which is integrally brazed in the nose of the nozzle to substantially encircle the melt bore which extends centrally therethrough.
Injection molding nozzles having integral electrical heating elements and methods of making them are well known in the art. For example, U.S. Pat. No. 4,768,945 to Schmidt which issued Sept. 6, 1988 and Canadian patent application Ser. No. 549,517 to Gellert filed Oct. 16, 1987 entitled "Method of Manufacture of Injection Molding Nozzle Having Grounded Heating Element Brazed into Pointed Tip" describe a nozzle and method of making it in which the integral heating element extends centrally into the pointed nose portion. The applicant's U.S. Pat. No. 4,768,283 which issued Sept. 6, 1988 discloses an earlier nozzle in which the forward end of the integral electrical heating element extends into the pointed nose portion. A further improvement on this type of nozzle having a pointed tip is shown in the applicant's Canadian patent application Ser. No. 563,981 filed Apr. 13, 1988 entitled "Injection Molding Nozzle Having Multiple Thickness Heating Element and Method of Manufacture".
With the continual development of more and more difficult to mold materials it is also well known to provide more heat closer to the gate area. For instance nozzles having a variety of heat conductive torpedoes are shown in the applicant's U.S. Pat. No. 4,279,588 which issued July 21, 1981 and 4,450,999 which issued May 29, 1984. Other examples are shown in U.S. Pat. No. 4,266,723 to Osuna-Diaz which issued May 12, 1981 and Mold-Masters Canadian patent application serial number 529,897 filed Feb. 17, 1987 entitled "Injection Molding System Having Manifold with Side Mounted Nozzles and Method" and Ser. No. 578,974 filed Sept. 30, 1988 entitled "Injection Molding Nozzle with Replaceable Gate Insert". Another development to respond to this problem is to provide a heated gate insert as shown in the applicant's Canadian patent application Ser. No. 559,000 filed Feb. 16, 1988 entitled "Injection Molding Heated Gate Insert and Method". While all of these previous nozzles represent considerable improvements, for certain applications and types of material it is still desirable to provide a nozzle having a central melt bore with additional heat in the gate area. Additional heat close to the gate is also very desirable when temperature assisted or thermal gating is being used as described in U.S. Pat. No. 4,768,945 referred to above.